High temperature superconducting (HTS) electrical motors, generators, and transformers can be significantly lighter in weight and smaller than their conventional counterpart machines. Continuing development of such machines is needed for use in advanced military and civilian equipment especially in the development of space and airborne systems where both weight and size considerations are of prime importance. The use of winding materials based on a flat uniform or filamented tape of high current density second generation superconductor materials such as yttrium barium copper oxide (YBCO, YBa2Cu3O7x) in the machine windings appears to offer a promising avenue toward machines of the needed types.
Two major shortcomings of superconductors, such as yttrium barium copper oxide coated superconductors, need to be overcome, however, in order to permit their widespread implementation into alternating current electrical machinery applications such as armature and field winding in motors and generators and transformer windings [1]. (Bracketed numbers such as this [1] refer to the list of reference documents appearing at the end of this specification; these documents and each other document identified in this text are hereby incorporated by reference herein.)
One issue associated with yttrium barium copper oxide coated conductors, manufactured in the form of thin and relatively wide tapes, for example, is the high hysteresis loss occurring when such a conductor is disposed in a time-varying magnetic field. Another issue concerns attendant mechanical properties of the conductor that are very different from the properties of traditional material such as copper Litz wire. Bending strain limitations restrict the types of winding configurations that are possible when such conductors are compared to copper. A route to hysteresis (and overall) loss reduction explored in recent years is replacement of the uniform wide yttrium barium copper oxide film with a set of parallel narrow filaments or stripes or striations [2-6]. Early work has suggested that in time the hysteresis loss in experimental multifilamentary samples can be reduced by at least an order of magnitude.
Notwithstanding such hysteresis loss improvement however, another type of loss specific to multifilamentary coated conductors—i.e., coupling loss—can become comparable in size to the hysteresis loss at a sweep rate Bf of a few Tesla per second when the conductor twist pitch is for example equal to 20 centimeters (here B is the amplitude of the magnetic field and f is the field change frequency) [1]. In order to achieve a substantial—i.e., one or two orders of magnitude—reduction in total losses (hysteresis and coupling) at an operating sweep rate of at least 10 Tesla per second, measures need to be taken to reduce both hysteresis and coupling losses.
Another shortcoming of coated superconductors is their low tolerance to bending and twisting strain. This conductor characteristic requires an almost complete reexamination of the winding techniques used with such conductors. The problems of alternating current losses and mechanical properties of the conductor become intertwined because twisting of the multifilamentary conductor is necessary in order to limit coupling losses. The present invention presents novel approaches to arranging magnets and coils with second generation superconductors such as yttrium barium copper oxide coated conductors.